The present invention relates to an improved process and apparatus for the destructive distillation or pyrolysis of rubber, such as used rubber tires, to produce liquid and gaseous hydrocarbons and a solid carbonaceous char. More particularly, the invention is directed to an improved process and apparatus for preheating a rubber charge introduced into a distillation oven, cooling the char produced therein, determining the distillation end point and providing a substantially gas-tight distillation oven door seal.
Disposal of discarded rubber tires poses a significant environmental problem. Burning of used tires is undesirable, if not prohibited, due to the attendant air pollution, while landfilling essentially nonbiodegradable rubber rapidly depletes available landfill space.
In devising ways to more effectively dispose of used tires, particular attention has been paid to methods for recovering the raw materials present in scrap rubber. Generally, it is known that scrap rubber may be heated in a sealed distillation oven substantially free of oxygen under conditions of pressure and temperature such that the rubber disassociates into a vapor phase comprising the volatilized hydrocarbon components of the rubber and a solid carbonaceous char. At least some of the vapor phase withdrawn from the oven is, condensed to form various liquid hydrocarbon fractions which are separated from the remaining gaseous hydrocarbons. Both the liquid and gaseous hydrocarbons may be used as fuel sources and may even be recycled to the destructive distillation process to provide some or all of the fuel burned to heat the rubber. After the destructive distillation is complete, the oven and its contents are cooled and the solid carbonaceous char is removed from the oven. After processing to remove any steel scrap, the solid material that remains may be used as carbon black in the production of new tires or as a component in roadway asphalt.
Jarrell, U.S. Pat. No. 5,230,777, discloses a vacuum destructive distillation process and apparatus for recovering hydrocarbon fuel and carbon black from rubber tires. Jarrell describes the operation of two rubber distillation ovens in off-set, batchwise distillation cycles and the conservation of energy by using waste heat removed from one of the ovens during cooling to preheat the rubber charge in the other oven. To achieve this, the two ovens are connected by a valved pressure equalization line. At the end of the distillation cycle in one of the ovens, the pressure in the other oven, which contains a fresh charge of rubber feed, is reduced to provide a pressure differential between the two ovens. The pressure equalization line is then opened to produce a one-way flow of gas between the two ovens until the pressure is equalized. As a result of the gas flow, the oven in which the distillation cycle has just been completed and the rubber char contained therein is cooled and a small amount of the waste heat transferred to the other oven. The transferred waste heat preheats the rubber feed in the other oven, thereby conserving energy by reducing the amount of heat necessary for the distillation.
Although Jarrell achieves a certain degree of energy recovery, gas flow and heat transfer essentially stops as soon as the pressure in the two ovens has equalized. As a result, the waste heat in the cooling oven is not fully utilized in preheating the rubber charge in the other oven, nor does the waste heat from the cooling oven dissipate at an effective rate. Since considerable time must pass to allow the oven and its contents to cool before it can be opened and reloaded with a rubber charge, the processing capacity of the system is limited. Another difficulty encountered in Jarrell and other prior art rubber distillation systems is the inability to accurately determine the end point of rubber pyrolysis so as to consistently obtain a char of desired composition. Furthermore, the door seals on ovens of destructive distillation apparatus often leak during operation due to thermal warping of the door and housing. Leaks in an oven door seal decrease the quality of the hydrocarbon vapor produced and compromise the safety of the apparatus.
Among the objects of the present invention, therefore, may be noted the provision of an apparatus and process for the destructive distillation of rubber to produce hydrocarbon and a solid carbonaceous char in which energy conservation is improved; the provision of such an apparatus and process in which the cooling time between distillation cycles is effectively reduced to increase the system""s processing capacity; the provision of such an apparatus and process in which the end point of rubber distillation can be easily and consistently determined; and the provision of an improved door seal for a destructive distillation oven which substantially inhibits the flow of air into the oven despite thermal warping of the door and housing.
Briefly, therefore, the present invention is directed to a process for the destructive distillation of rubber to produce hydrocarbon and a solid carbonaceous char. The process comprises heating rubber in the substantial absence of oxygen to a temperature sufficient to pyrolyze the rubber, distill a vapor comprising hydrocarbon from the rubber, and produce a solid carbonaceous char. The vapor produced is partially condensed to produce a liquid fraction comprising hydrocarbon and a remaining gaseous fraction. The carbonaceous char is contacted with a heat transfer gas to transfer heat from the char to the gas and thereby cool the char. The heat transfer gas circulates in a circulation loop which comprises means for removing the heat transferred to the gas from the char.
The invention is further directed to a process for the destructive distillation of rubber to produce hydrocarbon and a solid carbonaceous char. The process comprises loading a charge of rubber into a first distillation chamber and heating the rubber charge in the substantial absence of oxygen to a temperature sufficient to pyrolyze the rubber, distill a vapor comprising hydrocarbon from the rubber, and produce a solid carbonaceous char. The hydrocarbon containing vapor produced is partially condensed to produce a liquid fraction comprising hydrocarbon and a remaining gaseous fraction. A second charge of rubber is loaded into a second distillation chamber and a heat transfer gas is circulated between the first distillation chamber and the second distillation chamber so that the gas contacts carbonaceous char in the first chamber and contacts the second rubber charge in the second chamber. Circulation of the heat transfer gas results in heat being transferred from the carbonaceous char to the gas in the first chamber and heat being transferred from the gas to the second rubber charge in the second chamber, thereby cooling the char in the first chamber and preheating the second charge in the second chamber.
The invention is further directed to a process for the destructive distillation of rubber to produce hydrocarbon and a solid carbonaceous char. The process comprises heating a rubber charge in a distillation chamber in the substantial absence of oxygen to a temperature sufficient to pyrolyze the rubber, distill a vapor comprising hydrocarbon from the rubber charge and produce a solid carbonaceous char. The vapor produced is partially condensed to produce a liquid fraction comprising hydrocarbon and a remaining gaseous fraction. The weight loss of the rubber charge in the chamber as a result of pyrolysis is monitored and the heating of the rubber charge is discontinued in response to the weight loss of the rubber charge or a function of the weight loss of the rubber charge.
The invention is further directed to an apparatus for the destructive distillation of rubber to produce hydrocarbon and a solid carbonaceous char. The apparatus comprises a distillation chamber for holding the rubber. The chamber is sealable for the substantial exclusion of oxygen from the chamber. A heating means is associated with the distillation chamber for heating rubber in the chamber to a temperature sufficient to pyrolyze the rubber, distill a vapor comprising hydrocarbon from the rubber, and produce a solid carbonaceous char. Also included in the apparatus are means for removing the hydrocarbon-containing vapor from the chamber and means for condensing hydrocarbon from the vapor removed from the chamber to produce a liquid fraction comprising hydrocarbon. The apparatus further comprises means for circulating a heat transfer gas in a circulation loop, the heat transfer gas passing through the chamber and contacting the carbonaceous char to transfer heat from the char to the gas and thereby cool the char and means for removing heat from the heat transfer gas circulating in the circulation loop.
The invention is further directed to an apparatus for the destructive distillation of rubber to produce hydrocarbon and a solid carbonaceous char. The apparatus comprises two distillation chambers for holding the rubber. The chambers are sealable for the substantial exclusion of oxygen from the chambers. A heating means is associated with each distillation chamber for heating rubber in the chambers to a temperature sufficient to pyrolyze the rubber, distill a vapor comprising hydrocarbon from the rubber, and produce a solid carbonaceous char. Also included in the apparatus are means for removing the hydrocarbon-containing vapor from the chambers and means for condensing hydrocarbon from the vapor removed from the chambers to produce a liquid fraction comprising hydrocarbon. The apparatus further comprises means for circulating a heat transfer gas in a circulation loop, the heat transfer gas passing through both of the distillation chambers such that the gas contacts solid carbonaceous char in one of the chambers and contacts a rubber charge in the other chamber. Heat is thereby transferred from the carbonaceous char to the heat transfer gas in the one chamber to cool the char while heat is transferred from the gas to the rubber charge in the other chamber to preheat the charge.
The invention is further directed to an apparatus for the destructive distillation of rubber to produce hydrocarbon and a solid carbonaceous char. The apparatus comprises a distillation chamber for holding a rubber charge. The chamber is sealable for the substantial exclusion of oxygen from the chamber. A heating means is associated with the chamber for heating the rubber charge in the chamber to a temperature sufficient to pyrolyze the rubber, distill a vapor comprising hydrocarbon from the rubber, and produce a solid carbonaceous char. Also included in the apparatus are means for removing the hydrocarbon-containing vapor from the chamber and means for condensing hydrocarbon from the vapor to produce a liquid fraction comprising hydrocarbon. The apparatus further comprises means for monitoring weight loss of the rubber charge in the chamber as a result of pyrolysis.
The invention is further directed to a pyrolysis oven comprising a housing defining an internal distillation chamber, an opening in the housing providing access to the distillation chamber. A door adjacent the housing is movable between closed and open positions. In the closed position the door substantially covers the opening and a gap is defined between the door and the housing. In the open position the door is positioned away from the opening to provide access to the distillation chamber through the opening. An inflatable sealing tube member, generally annular in shape, is attached to one of the door and the housing adjacent the periphery of the opening so that the tube member is disposed within the gap when the door is in its the closed position. The oven further comprises means for introducing a fluid into the sealing tube member to inflate the tube member so that it sealingly engages the other of the door and the housing around the opening when the door is in its the closed position.
Other objects and features of this invention will be in part apparent and in part pointed out hereinafter.